This or That? for my list

I like a lot of names, but many of them could not be used together. I would love to hear some Berry opinions that would help me get a broader perspective on which names are "better" in all these pairs. Also, if you could give reasons why you prefer one over the other, that would be really helpful!

Simeon or Gideon? Both are wonderful but I slightly prefer Gideon. Simeon sounds similar to simian (ape-like) which is worrisome.Gideon or Gable? - Gideon for its Biblical history and spunky vibe! Gable is better in the middle spot.Malachi or Mordecai? - Malachi gets my vote! Mordecai reminds me of mortification.
Hugh or Hugo? - I love the European flair of Hugo and you get to use Hugh as a nn (it's two names in one ).
Cobalt or Roan? - Roan is similar to Rowan and Ronan so it "sounds" like a name. Cobalt is trying too hard.Will or Shale? - I like Will more than William but I'm sure I'm in the minority here on Nameberry. Shale is a word that doesn't translate well into a person's name.

Girls:

Willa or Della? - Willa for its literary connection. I don't like Della, Ella or Bella.Willa or Willow? - I like Willa for a first name and Willow as a middle name.
Adelaide or Adeline? - I love both names but prefer the vintage charm of Adeline.Lilac or Lark? - Lilac is a guilty pleasure of mine. I like Lark too.
Fern or Wren? - I love the softness of Wren.
Moriah or Sarai? - I like both names but Sarai won out! Moriah is too close to Mariah Carey.Melora or Moriah? - I like Melora for its lush and romantic sound.Marilla or Marcella? - A classic Roman beauty.
Cadence or Carys? - Neither is a fave but Carys is less trendy than Cadence.Ruby or Pearl? - I love both names but the spunky Ruby wins by a hair!Delaney or Connelly? - Neither is my style but Delaney actually "sounds" like a first name.
Eliora or Eleni? - Eleni is one of my favourite Greek names.
Annika or Azalea? - A more exotic flower choice.Verity or Vivienne? - I love both names but I have a huge crush on Verity at the moment. I prefer the Vivian spelling.Eliza or Elsa? - I love both names but I chose the spunky and sassy Eliza.

Girls/boys (The name on the left I would use for a girl, the name on the right I would use for a boy. I just couldn't use both.):

Hazel or Gable? - Hazel for sure! Gable would be an interesting mn choice for a boy.Ruby or Reuben? - I love both names but Ruby has too much spunk for me to pass up.
Cadence or Kenyon? - Kenyon is certainly less trendy than Cadence.If you think you'll have a blond boy, Kenyon would be a great choice.

Wow, Mischa, your post was very helpful! It confirmed many of my misgivings about certain names (ex. Mordecai sounding so close to "mortified," Cadence coming across as trendy) and gave me some great new ideas. I am really loving the idea of Gable as a middle name (and I could still use Hazel, yay!) and Willow as a middle name makes sense. Also, thanks for the commentary on the names!